This invention relates to a coating resin and an antifouling coating composition to be used for preventing attachment of marine organisms to the underwater or submarine structures such as ships, fishing nets, drainage conduits, etc.
Numerous species of marine organisms, such as barnacle, ascidian, serpula, mussel, laver, etc., live in the sea water. When a structure such as a ship, fishing net, drainage pipe, etc., is set or placed in comission in or on the sea, the marine organisms cling to the structure and grow to give various kinds of damage to the structure. For instance, if the ship's bottom is incrusted with marine organisms, the frictional resistance of the sea water increases to cause a reduction of cruising performance of the ship, so that if it is tried to keep a constant cruising speed of the ship, its fuel consumption increases to pose a serious encomical problem. Also, if the marine organisms cling to the fishing nets used for ocean culture, the meshes of the nets would be clogged up, which could prove fatal to the cultured fishes and shellfishes.
Hitherto, in order to prevent attachment of the marine organisms to the underwater structures such as mentioned above, the antifouling paints using single polymers or copolymers of organotin-containing unsaturated monomers as resinous component (see Japanese Patent Application Kokoku (Post-Exam Publication) Nos. 40-21426, 44-9579, 46-13392, 49-20491, 51-11647, 51-12049, 52-48170, etc.) have been applied to said structures. These polymers have their organotin portion hydrolyzed with the sea water (pH: 8.0-8.3). As a result, not only the organotin serves as an antifouling agent, but also the polymer surface which has been made soluble in sea water is gradually corroded by the moving sea water to bare out the new coating surface, thus producing a long-lasting stabilized antifouling effect. However, the organotin released into the sea water from the paints is hard to decompose and may be taken in by and accumulated in the marine organisms and, through the food chain, it may get into the human system. This involves the possibility of causing serious physical trouble such as deformity. So, use of organotin in the antifouling paints has been banned.
Request is now voiced in the art for the development of a resin for antifouling paints which are capable of producing a long-lasting stabilized antifouling effect, in place of the organotin-based resins whose use has been banned. Ideally speaking, it is desirable that the resins used for antifouling paints are of a hydrolyzable type like the organotin-based resins, but proposals involving use of hydrophilic or water-repellent resins have also been made (Japanese Patent Application Kokai (Laid-Open) Nos. 62-290768, 62-13471, 58-180566, 57-67672, etc.). However, it is hardly possible to realize a long-lasting stabilized antifouling effect by use of a resin having the hydrophilic or water-repellent property alone.
In view of the above, various hydrolyzable resins having a specific carboxylic acid ester in the side chain have been proposed (WO 84/02915, Japanese Patent Appln. Kokai Nos. H2-69576, 63-215780, 62-57464, Japanese Patent Appln. Kokoku Nos. 55-39271, 61-3830, etc.), but their effect has not been well satisfactory.
It is essential that the resin used for said purpose is soluble in the aromatic solvents or the mixtures of aromatic solvents (main solvent) and other types of solvent such as alcohol type solvents, ketone type solvents, halogen type solvents, ether type solvents and ester type solvents so that the solvent used won't affect the undercoat when coating is performed.